U.S. patent application number 09/737848 was filed with the patent office on 2001-06-21 for semicrystalline propylene polymer compositions with good suitability for producing biaxially oriented films.
Invention is credited to Bidell, Wolfgang, Hingmann, Roland, Langhauser, Franz, Lilge, Dieter, Rauschenberger, Volker, Schweier, Gunther, Stricker, Florian, Suhm, Jurgen.
Application Number | 20010004662 09/737848 |
Document ID | / |
Family ID | 7933883 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010004662 |
Kind Code |
A1 |
Bidell, Wolfgang ; et
al. |
June 21, 2001 |
Semicrystalline propylene polymer compositions with good
suitability for producing biaxially oriented films
Abstract
A semicrystalline propylene polymer composition with good
suitability for producing biaxially oriented films and prepared by
polymerizing propylene, ethylene and/or C.sub.4-C.sub.18-1-alkenes,
where at least 50 mol % of the monomer units present arise from the
polymerization of propylene, the use of the semicrystalline
propylene polymer composition for producing films, fibers or
moldings, the films, fibers and moldings made from these
compositions, biaxially stretched films made from the
semicrystalline propylene polymer compositions, and also a method
for characterizing the semicrystalline propylene polymer
compositions.
Inventors: |
Bidell, Wolfgang;
(Mutterstadt, DE) ; Hingmann, Roland; (Sant Just
Desvern (Barcelona), ES) ; Langhauser, Franz;
(Ruppertsberg, DE) ; Lilge, Dieter; (Limburgerhof,
DE) ; Rauschenberger, Volker; (Eisenberg, DE)
; Schweier, Gunther; (Friedelsheim, DE) ;
Stricker, Florian; (Heidelberg, DE) ; Suhm,
Jurgen; (Ludwigshafen, DE) |
Correspondence
Address: |
Messrs. Keil & Weinkauf
1101 Connecticut Ave., N.W.
Washington
DC
20036
US
|
Family ID: |
7933883 |
Appl. No.: |
09/737848 |
Filed: |
December 18, 2000 |
Current U.S.
Class: |
526/348 ;
526/348.2; 526/348.3; 526/348.4; 526/348.5; 526/348.6 |
Current CPC
Class: |
C08F 297/08 20130101;
C08F 10/06 20130101; Y10S 428/91 20130101; Y10S 264/901 20130101;
C08F 210/06 20130101; C08F 4/65916 20130101; C08F 110/06 20130101;
C08F 4/65927 20130101; C08L 2314/06 20130101; C08F 210/16 20130101;
C08L 2666/04 20130101; C08F 2500/26 20130101; C08F 2/001 20130101;
C08F 210/06 20130101; C08F 4/65904 20130101; C08F 2500/26 20130101;
C08F 10/06 20130101; C08F 110/06 20130101; C08L 23/14 20130101;
Y10S 526/905 20130101; C08L 23/14 20130101; C08F 10/06 20130101;
C08F 4/65908 20130101; C08L 2205/02 20130101 |
Class at
Publication: |
526/348 ;
526/348.2; 526/348.3; 526/348.4; 526/348.5; 526/348.6 |
International
Class: |
C08F 210/06; C08F
010/02; C08F 010/04; C08F 210/02; C08F 210/14; C08F 210/16; C08F
210/04; C08F 010/06; C08F 010/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 1999 |
DE |
19962130.6 |
Claims
We claim:
1. A semicrystalline propylene polymer composition with good
suitability for producing biaxially oriented films and prepared by
polymerizing propylene, ethylene and/or C.sub.4-C.sub.18-1-alkenes,
where at least 50 mol % of the monomer units present arise from the
polymerization of propylene, and with a melting point T.sub.M of
from 65 to 170.degree. C., where the melting point T.sub.M is
determined by Differential Scanning Calorimetry (DSC) to ISO 3146
by heating a previously melted specimen at a heating rate of
20.degree. C./min, and is measured in .degree.C., and is the
maximum of the resultant curve, and where the semicrystalline
propylene polymer composition can be broken down into from 40 to
85% by weight of a principal component A, from 0 to 55% by weight
of an ancillary component B, and from 0 to 55% by weight of an
ancillary component C, where the proportions of components A, B and
C are determined by carrying out TREF (temperature rising elution
fractionation) in which the polymers are firstly dissolved in
boiling xylene and the solution is then cooled at a cooling rate of
10.degree. C./h to 25.degree. C., and then, as the temperature
rises, that fraction of the propylene polymer composition which is
soluble in xylene at (T.sub.M/2)+7.5.degree. C. is then dissolved
and separated off from the remaining solid, and then, as the
temperature rises, at all of the higher temperatures 70.degree. C.,
75.degree. C., 80.degree. C., 85.degree. C., 90.degree. C.,
94.degree. C., 98.degree. C., 102.degree. C., 107.degree. C.,
112.degree. C., 117.degree. C., 122.degree. C. and 125.degree. C.
the fractions soluble within the temperature range between this
elution temperature and the preceding elution temperature are
eluted, and the fractions taken into consideration during the
evaluation which follows are those whose proportion by weight is at
least 1% by weight of the initial weight of the propylene polymer
composition specimen, and gel permeation chromatography (GPC) at
145.degree. C. in 1,2,4-trichlorobenzene is used to measure the
molar mass distribution of all of the fractions to be taken into
consideration, and the principal component A is formed by all of
the fractions which are eluted at above (T.sub.M/2)+7.5.degree. C.
and have an average molar mass M.sub.n (number
average).gtoreq.120,000 g/mol, the ancillary component B is formed
by the fraction which is eluted at (T.sub.M/2)+7.5.degree. C., and
the ancillary component C is formed by all of the fractions to be
taken into consideration which are eluted at above
(T.sub.M/2)+7.5.degree. C. and have an average molar mass M.sub.n
(number average)<120,000 g/mol, and where at least one of the
fractions forming the principal component A has a ratio between
weight-average (M.sub.w) and number-average (M.sub.n) molar masses
of the polymers M.sub.w/M.sub.n>4.5.
2. A semicrystalline propylene polymer composition as claimed in
claim 1, where the fractions forming the principal component A and
having a ratio M.sub.w/M.sub.n>4.5 make up at least 10% by
weight of the principal component A.
3. A semicrystalline propylene polymer composition as claimed in
claim 1, which can be broken down into from 55 to 75% by weight of
the principal component A, from 5 to 20% by weight of the ancillary
component B, and from 10 to 35% by weight of an ancillary component
C.
4. A semicrystalline propylene polymer composition with good
suitability for producing biaxially oriented films and prepared by
polymerizing propylene, ethylene and/or C.sub.4-C.sub.18-1-alkenes,
where at least 50 mol % of the monomer units present arise from the
polymerization of propylene, and with a melting point T.sub.M of
from 65 to 170.degree. C., where the melting point T.sub.M is
determined by Differential Scanning Calorimetry (DSC) to ISO 3146
by heating a previously melted specimen at a heating rate of
20.degree. C./min, and is measured in .degree.C., and is the
maximum of the resultant curve, and where the semicrystalline
propylene polymer composition can be broken down into from 40 to
85% by weight of a principal component A, from 0 to 55% by weight
of an ancillary component B, and from 0 to 40% by weight of an
ancillary component C, where the proportions of components A, B and
C are determined by carrying out TREF (temperature rising elution
fractionation) in which the polymers are firstly dissolved in
boiling xylene and the solution is then cooled at a cooling rate of
10.degree. C./h to 25.degree. C., and then, as the temperature
rises, that fraction of the propylene polymer composition which is
soluble in xylene at (T.sub.M/2)+7.5.degree. C. is then dissolved
and separated off from the remaining solid, and then, as the
temperature rises, at all of the higher temperatures 70.degree. C.,
75.degree. C., 80.degree. C., 85.degree. C., 90.degree. C.,
94.degree. C., 98.degree. C., 102.degree. C., 107.degree. C.,
112.degree. C., 117.degree. C., 122.degree. C. and 125.degree. C.
the fractions soluble within the temperature range between this
elution temperature and the preceding elution temperature are
eluted, and the fractions taken into consideration during the
evaluation which follows are those whose proportion by weight is at
least 1% by weight of the initial weight of the propylene polymer
composition specimen, and gel permeation chromatography (GPC) at
145.degree. C. in 1,2,4-trichlorobenzene is used to measure the
molar mass distribution of all of the fractions to be taken into
consideration, and the principal component A is formed by all of
the fractions to be taken into consideration and which are eluted
at above (T.sub.M/2)+7.5.degree. C. and have an average molar mass
M.sub.n (number average).gtoreq.120,000 g/mol, the ancillary
component B is formed by the fraction which is eluted at
(T.sub.M/2)+7.5.degree. C., and the ancillary component C is formed
by all of the fractions to be taken into consideration and which
are eluted at above (T.sub.M/2)+7.5.degree. C. and have an average
molar mass M.sub.n (number average)<120,000 g/mol, and where the
room-temperature xylene-soluble fraction X.sub.L in the
semicrystalline propylene polymer composition is not more than 5%
by weight.
5. A semicrystalline propylene polymer composition as claimed in
claim 4, where the room-temperature xylene-soluble fraction X.sub.L
is not more than 3% by weight.
6. A semicrystalline propylene polymer composition as claimed in
claim 4, which can be broken down into from 50 to 70% by weight of
the principal component A, from 20 to 35% by weight of the
ancillary component B, and from 5 to 30% by weight of an ancillary
component C.
7. A film, a fiber or a molding comprising semicrystalline
propylene polymer compositions as claimed in claim 1.
8. A biaxially stretched film made from the semicrystalline
propylene polymer compositions as claimed in claim 1 and having a
stretching ratio of at least 1:3 longitudinally and of at least 1:5
transversely.
9. A method for characterizing semicrystalline propylene polymer
compositions in relation to their suitability for producing
biaxially oriented films, which comprises determining the melting
point T.sub.M of the propylene polymer compositions, using TREF
(Temperature Rising Elution Fractionation) to separate the
propylene polymer compositions into fractions of different
crystallizability and determining the molar mass distribution of
these, and using these data to divide the semicrystalline propylene
polymer compositions into a relatively highly crystalline,
higher-molecular-weight principal component A, a low-crystallinity
ancillary component B and a relatively highly crystalline,
low-molecular-weight ancillary component C.
10. A film, a fiber or a molding comprising semicrystalline
propylene polymer compositions as claimed in claim 4.
11. A biaxially stretched film made from the semicrystalline
propylene polymer compositions as claimed in claim 4 and having a
stretching ratio of at least 1:3 longitudinally and of at least 1:5
transversely.
Description
[0001] The present invention relates to semicrystalline propylene
polymer compositions which are particularly suitable for producing
biaxially oriented films. The invention further relates to the use
of the semicrystalline propylene polymer compositions for producing
films, fibers or moldings, and also to the films, fibers and
moldings made from these compositions.
[0002] The term polypropylene is generally understood to denote a
wide variety of different polymers, a common feature of which is
that they have been built up to a substantial extent from the
monomer propylene. The various polypropylenes are generally
obtained by coordinative polymerization on catalysts made from
transition metals, which give predominantly ordered incorporation
of the monomers into a growing polymer chain.
[0003] The polymer chains obtained during the polymerization of
propylene with the usual coordination catalysts have a methyl side
group on each second carbon atom. The polymerization therefore
proceeds in a regioselective manner. Depending on the orientation
of the monomers during incorporation into the chain, various
stereochemical configurations are obtained. If the monomers all
have the same arrangement when they are incorporated, the methyl
side groups in the polymer chain are then all on the same side of
the principal chain. The term used is isotactic polypropylene. If
all of the monomers alternate in their spatial orientation when
incorporated into the chain, the resultant polypropylene is termed
syndiotactic. Both of these varieties with their stereoregular
structures are semicrystalline and therefore have a melting
point.
[0004] However, since the incorporation of the propylene monomers
when coordination catalysts are used is not absolutely consistent,
but some of the monomers are introduced in a way which differs from
that of the majority, the polymer chains formed always have
"defects" in the prevailing arrangement, and the number of these
defects can vary considerably.
[0005] The longer the defect-free structure sequences in the
polymer chains, the more readily the chains crystallize and
therefore the higher are the crystallinity and the melting point of
the polypropylene.
[0006] If the methyl side groups have an irregular stereochemical
arrangement the polypropylenes are termed atactic. These are
completely amorphous and therefore have no melting point.
[0007] The industrial preparation of polypropylene nowadays mostly
uses heterogeneous catalysts based on titanium, and the resultant
product is a predominantly isotactic polymer. These catalysts, for
which the term Ziegler-Natta catalysts has become established, have
a number of different centers active for polymerization. These
centers differ both in their stereospecificity, i.e. in the number
of "defects" which the resultant chains have, and also in the
average molar mass of the chains formed. The predominant defects
observed in all cases are stereo-defects, meaning that individual
propylene monomers were incorporated syndiospecifically instead of
isospecifically. The result of polymerization with heterogeneous
catalysts of this type is therefore a mixture of various polymer
chains which differ both in their stereochemistry and in their
molar mass.
[0008] A substantial application sector for polypropylenes is that
of films, particularly biaxially stretched films, frequently also
termed BOPP (biaxially oriented polypropylene) films.
[0009] A general aim of almost all developments in the
polypropylenes sector is to reduce the soluble fractions of the
polymers used. This is frequently possible via the use of optimized
conventional Ziegler-Natta catalysts. The result is firstly an
improvement in organoleptic properties, advantageous for
applications in the medical and food sectors, and secondly a
favorable effect on mechanical properties, in particular stiffness.
However, polypropylenes of this type with reduced soluble fractions
cannot be used for producing biaxially stretched polypropylene
films, since they have low capability, or no capability, for
processing to give these films. Many efforts have therefore been
made to use variations in the composition in order to find
polypropylenes suitable for producing biaxially stretched
polypropylene films.
[0010] EP-A 339 804 describes a mixture of a homopolypropylene and
a random propylene copolymer, where the comonomer has been
incorporated within the upper range of the molecular-weight
distribution of the mixture. Mixtures of this type have good
optical and mechanical properties, but have limited
processibility.
[0011] EP-A 115 940 discloses propylene-ethylene copolymers
suitable for producing biaxially stretched films and having from
0.1 to 2.0 mol % of ethylene and high isotacticity. These polymers
have good extensibility, stiffness, transparency, impact strength
and stability in relation to heat-shrinkage. However, they
frequently do not meet the requirements of BOPP film producers with
respect to mechanical, Theological and optical properties.
[0012] EP-A 657 476 describes an .alpha.-olefin polymer obtained by
polymerizing an a-olefin having 3 or more carbon atoms and whose
composition has been defined via the proportions by weight of
fractions soluble in xylene at 20.degree. C. and insoluble in
xylene at 105.degree. C.
[0013] JP-A 10 053 675 describes a polypropylene composition
composed of a high-molecular-weight crystalline polypropylene with
a soluble fraction of less than 5% and a low-molecular-weight
polyolefin composition with a soluble fraction of more than
30%.
[0014] Although the propylene polymer compositions known from the
prior art permit the production of biaxially oriented polypropylene
films, they do not combine this property with ideal processibility
and very good mechanical properties of the films. This means that
it has hitherto not been possible to decouple the inverse
correlation between processibility and mechanical properties of the
films.
[0015] It is an object of the present invention, therefore, to
develop propylene polymer compositions which have excellent
processibility to give biaxially stretched films and from which, at
the same time, films with very good mechanical and optical
properties can be produced. It should also be possible to obtain
these by a very uncomplicated process, and the films should have
good barrier action, for example with respect to oxygen and water
vapor.
[0016] We have found that this object is achieved by a
semicrystalline propylene polymer composition with good suitability
for producing biaxially oriented films and prepared by polymerizing
propylene, ethylene and/or C.sub.4-C.sub.18-1-alkenes, where at
least 50 mol % of the monomer units present arise from the
polymerization of propylene,
[0017] and with a melting point T.sub.M of from 65 to 170.degree.
C., where the melting point T.sub.M is determined by differential
scanning calorimetry (DSC) to ISO 3146 by heating a previously
melted specimen at a heating rate of 20.degree. C./min, and is
measured in .degree.C. and is the maximum of the resultant
curve,
[0018] and where the semicrystalline propylene polymer composition
can be broken down into
[0019] from 40 to 85% by weight of a principal component A,
[0020] from 0 to 55% by weight of an ancillary component B, and
[0021] from 0 to 55% by weight of an ancillary component C,
[0022] where the proportions of components A, B and C are
determined by carrying out TREF (temperature rising elution
fractionation) in which the polymers are firstly dissolved in
boiling xylene and the solution is then cooled at a cooling rate of
10.degree. C./h to 25.degree. C., and then, as the temperature
rises, that fraction of the propylene polymer composition which is
soluble in xylene at (T.sub.M/2)+7.5.degree. C. is then dissolved
and separated off from the remaining solid, and then, as the
temperature rises, at all of the higher temperatures 70.degree. C.,
75.degree. C., 80.degree. C., 85.degree. C., 90.degree. C.,
94.degree. C., 98.degree. C., 102.degree. C., 107.degree. C.,
112.degree. C., 117.degree. C., 122.degree. C. and 125.degree. C.
the fractions soluble within the temperature range between this
elution temperature and the preceding elution temperature are
eluted, and the fractions taken into consideration during the
evaluation which follows are those whose proportion by weight is at
least 1% by weight of the initial weight of the propylene polymer
composition specimen, and gel permeation chromatography (GPC) at
145.degree. C. in 1,2,4-trichlorobenzene is used to measure the
molar mass distribution of all of the fractions to be taken into
consideration,
[0023] and the principal component A is formed by all of the
fractions which are eluted at above (T.sub.M/2)+7.5.degree. C. and
have an average molar mass M.sub.n (number average).gtoreq.120,000
g/mol,
[0024] the ancillary component B is formed by the fraction which is
eluted at (T.sub.M/2)+7.5.degree. C., and
[0025] the ancillary component C is formed by all of the fractions
to be taken into consideration and which are eluted at above
(T.sub.M/2)+7.5.degree. C. and have an average molar mass M.sub.n
(number average)< 120,000 g/mol,
[0026] and where at least one of the fractions forming the
principal component A has a ratio between weight-average (M.sub.w)
and number-average (M.sub.n) molar masses of the polymers
M.sub.w/M.sub.n>4.5.
[0027] In addition, semicrystalline propylene polymer compositions
have been found which have good suitability for producing biaxially
oriented films and are prepared by polymerizing propylene, ethylene
and/or C.sub.4-C.sub.18-1-alkenes, where at least 50 mol % of the
monomer units present arise from polymerizing propylene, and the
compositions have a melting point TM of from 65 to 170.degree.
C.,
[0028] where the semicrystalline propylene polymer composition can
be broken down into
[0029] from 40 to 85% by weight of a principal component A,
[0030] from 15 to 55% by weight of an ancillary component B,
and
[0031] from 0 to 40% by weight of an ancillary component C,
[0032] and the room-temperature xylene-soluble fraction X.sub.L of
the semicrystalline propylene polymer composition is not more than
5% by weight.
[0033] The use of the semicrystalline propylene polymer composition
for producing films, fibers or moldings has also been found, as
have the films, fibers and moldings made from this composition.
[0034] The novel semicrystalline propylene polymer compositions are
prepared by polymerizing propylene, ethylene and/or
C.sub.4-C.sub.18-1-alkenes. For the purposes of the present
invention, C.sub.4-C.sub.18-1-alkenes are linear or branched
1-alkenes which have from 4 to 18 carbon atoms. Preference is given
to linear 1-alkenes, and particular mention is made of ethylene,
1-butene, 1-pentene, 1-hexene, 1-heptene and 1-octene and mixtures
made from these comonomers, and preference is given to the use of
ethylene or 1-butene. The propylene polymer compositions comprise
at least 50 mol % of monomer units which arise from polymerizing
propylene. The content of propylene-derived monomer units is
preferably at least 70 mol % and in particular at least 85 mol %.
In another preferred embodiment, propylene is the sole monomer used
in preparing the novel propylene polymer compositions, meaning that
the polymer is a propylene homopolymer. If use was made of one or
more comonomers it may be that the entire propylene polymer
composition has substantially the same comonomer distribution, like
that of random copolymers. However, it may also be that, as in what
are known as propylene impact copolymers, there is a mixture of
different components which have different comonomer contents.
[0035] The novel semicrystalline propylene polymer compositions
have melting points T.sub.M of from 65 to 170.degree. C.,
preferably from 135 to 165.degree. C.
[0036] For the purposes of the present invention, the melting point
T.sub.M is the temperature of the maximum of the plot of enthalpy
against temperature for a previously melted specimen heated at a
heating rate of 20.degree. C./min obtained using differential
scanning calorimetry (DSC) to ISO 3146. The DSC measurement here is
usually carried out by first heating the specimen at a heating rate
of 20.degree. C./min to about 40.degree. C. above the melting
point, then allowing the specimen to undergo dynamic
crystallization at a cooling rate of 20.degree. C./min and then
determining the melting point T.sub.M during a second heating
procedure at a heating rate of 20.degree. C./min.
[0037] To determine the proportions of components A, B and C in the
semicrystalline propylene polymer compositions, according to the
invention a fractionation is carried out using TREF (temperature
rising elution fractionation) and the molar mass distribution of
all of the fractions is then measured by gel permeation
chromatography (GPC).
[0038] GPC and TREF are methods for using various physical
properties to fractionate polymer specimens. While GPC fractionates
polymer chains by their size, the separation in TREF is by
crystallizability of the polymer molecules. The principle of
temperature rising elution fractionation was described in detail in
L. Wild, Advances in Polymer Sciences 98, 1 - 47 (1990), by way of
example. In this technique, a polymer specimen is dissolved in a
solvent at an elevated temperature, and the concentration of the
solution should be below 2% by weight. The polymer solution is then
cooled very slowly (about 0.1.degree. C./min). The first polymer
molecules to precipitate are then those which crystallize very
well, and these are followed by molecules with poorer
crystallization properties. In the polymer particles produced in
the solvent, therefore, the crystallizability of the molecules of
which these particles are composed decreases from the inside toward
the outside. The cooling is followed by the actual fractionation by
heating the polymer suspension. During this process, the molecules
which crystallize poorly, located on the periphery of the polymer
particles, are first dissolved at a relatively low temperature and
are removed with the solvent which has dissolved them, followed at
a higher temperature by the polymer chains which crystallize more
readily.
[0039] The apparatus shown diagrammatically in FIG. 1 has proven
particularly suitable for carrying out TREF. This is composed of a
temperature-controllable storage tank (1), a
temperature-controllable elution vessel (2), two thermostats (3)
(type HC5 from Julabo, for example), two temperature sensors (4)
and a high-performance mixer (5) with which the polymer suspension
is mixed. In the lower part of the elution vessel, separated off by
wire netting, there is glass wool (6) which prevents undissolved
polymer particles from being discharged when polymer solutions are
run off.
[0040] According to the invention, to characterize semicrystalline
propylene polymer compositions the polymer is first dissolved in
xylene. In principle it is possible here to use any xylene isomer,
isomer mixture or isomer mixture with ethylbenzene content, and for
economic reasons isomer mixtures are preferred. However, it is
advantageous to avoid use of pure p-xylene and of isomer mixtures
with a p-xylene content of more than about 50% by weight, since
p-xylene freezes at about 20.degree. C.
[0041] To dissolve the polymer specimen it is placed, for example,
together with the solvent in a glass vessel with a magnetic stirrer
rod, underneath a reflux condenser, and the glass vessel is then
heated in a temperature-controllable bath with stirring until the
polymer has dissolved completely. The polymer solution is then
cooled, e.g. by dipping the glass vessel into the preheated oil
bath of a thermostat system, at a cooling rate of 10.degree. C./h
until room temperature has been reached. The specified cooling may
be achieved by appropriately programming a programmer associated
with the thermostat system. 5 g of propylene polymer are usually
dissolved in 400 ml of xylene for each TREF analysis.
[0042] The polymer suspension resulting from the specified
crystallization procedure is transferred into the elution vessel
(2) of the apparatus shown in FIG. 1, the temperature is raised to
(T.sub.M/2)+7.5.degree. C. and the polymer crystals are extracted
at this temperature for 15 minutes with vigorous mixing. The
polymer solution is then run off, while the crystals remain in the
extractor. The dissolved polymer is preferably precipitated in cold
acetone (at <0.degree. C.), filtered off and dried for from 4 to
5 hours at 100.degree. C. in vacuo.
[0043] 400 ml of xylene which has been temperature-controlled to
the next higher of the temperatures 70.degree. C., 75.degree. C.,
80.degree. C., 85.degree. C., 90.degree. C., 94.degree. C.,
98.degree. C., 102.degree. C., 107.degree. C., 112.degree. C.,
117.degree. C., 122.degree. C. and 125.degree. C. are then added to
the polymer crystals in the elution vessel (2), followed again by
mixing for 15 minutes at this next higher temperature. This
dissolves those fractions of the semicrystalline propylene polymer
composition which are soluble within the temperature range between
this elution temperature and the preceding elution temperature. The
resultant solution is then run off, while the crystals remain in
the extractor.
[0044] This process is repeated until all of the polymer crystals
have been dissolved. This stage was achieved at 125.degree. C. or
below in the case of all the polypropylenes studied so far.
[0045] The dissolved polymers from each of the fractions are
preferably precipitated in cold acetone (<0.degree. C.),
filtered off and dried for from 4 to 5 hours at 100.degree. C. in
vacuo.
[0046] Since there are some losses during the fractionation of any
polymer composition, even though the losses may be slight, the
amounts of the fractions generally give a total which is less than
the initial weight of the polymer specimen. This phenomenon can be
ignored as long as at least 96% of the initial weight of the
propylene polymer composition is retrieved in the fractions.
However, if the loss is higher, the fractionation must be
repeated.
[0047] It is also not possible to determine the molar mass
distribution reliably if the amounts of specimen used are extremely
small. To minimize error, the fractions to be taken into
consideration in carrying out the evaluation which follows to
calculate the amounts of components A, B and C are only those whose
proportion of the initial polymer specimen weight is at least 1% by
weight. The molar mass distribution of these fractions is
determined by gel permeation chromatography (GPC) in
1,2,4-trichlorobenzene at 145.degree. C., calibrating the GPC with
polypropylene standards with molar masses of from 100 to 10.sup.7
g/mol.
[0048] The fractions can then be allocated to each of the
components A, B and C according to the temperature at which the
respective fraction was eluted, i.e. the temperature within the
temperature sequence 70.degree. C., 75.degree. C., 80.degree. C.,
85.degree. C., 90.degree. C., 94.degree. C., 98.degree. C.,
102.degree. C., 107.degree. C., 112.degree. C., 117.degree. C.,
122.degree. C. at which the polymer chains dissolved, and according
to the average molar mass M.sub.n (number average) of the
respective fraction.
[0049] The principal component A is formed by all of the fractions
to be taken into consideration and which are eluted at above
(T.sub.M/2)+7.5.degree. C. and have an average molar mass M.sub.n
(number average).gtoreq. 120,000 g/mol.
[0050] The ancillary component B is formed by the fraction which is
eluted at (T.sub.M/2)+7.5.degree. C. If the proportion of the
fraction eluted at (T.sub.M/2)+7.5.degree. C. is less than 1% by
weight of the entire propylene polymer composition, the proportion
of the ancillary component B is 0% by weight according to the
definition given above for the fractions to be taken into
consideration.
[0051] The ancillary component C is formed by all of the fractions
to be taken into consideration which are eluted at above
(T.sub.M/2)+7.5.degree. C. and have an average molar mass M.sub.n
(number average)<120,000 g/mol.
[0052] Because of the losses during TREF and because fractions
whose proportion of the propylene polymer composition is less than
1% by weight are not given any further consideration, the amounts
of components A, B and C obtained experimentally give a total which
is less than the initial weight of polymer taken for fractionation
and used as a basis. Since the proportions of components A, B and C
are usually given in % by weight, the total of the proportions of
components A, B and C therefore differs from 100% by weight. This
difference may be termed Z and quantified by the formula
z=100% by weight-(A+B+C)
[0053] where A, B and C are the ratio of the amounts found of
components A, B and C to the initial weight of the propylene
polymer composition specimen in % by weight and Z is also given in
% by weight.
[0054] To interpret the good properties of the novel propylene
polymer compositions, it can be assumed that in particular a high
content of principal component A brings about high stiffness in the
films. The content of ancillary component B affects the processing
speed, and the content of ancillary component C has the task of
providing a broad range of temperature latitude.
[0055] Another variable for characterizing the novel propylene
polymer compositions is the room-temperature xylene-soluble
fraction XL, which for the purposes of the present invention is the
fraction determined by a method similar to that of ISO 1873-1:1991.
For this, 5 g of polypropylene are placed into 500 ml of distilled
xylene previously heated to 100.degree. C. The mixture is then
heated to the boiling point of the xylene and held for 60 min at
this temperature. Then, within a period of 20 min, the mixture is
cooled to 5.degree. C. using a cooling bath and then reheated to
20.degree. C., and this temperature is held for 30 min. The
precipitated polymer is filtered off. Precisely 100 ml of the
filtrate are drawn off and the solvent removed on a rotary
evaporator. The residue is dried for about 2 h at 80.degree.60
C./250 mbar to constant weight and weighed after cooling.
[0056] The xylene-soluble fraction is calculated as 1 X L = g
.times. 500 .times. 100 G .times. V
[0057] where
[0058] X.sub.L=xylene-soluble fraction in %,
[0059] g amount found in g,
[0060] G=initial weight of product in g, and
[0061] V=volume of filtrate used in ml.
[0062] In one embodiment of the present invention the novel
semicrystalline propylene polymer compositions can be broken down
into
[0063] from 40 to 85% by weight, preferably from 50 to 80% by
weight and in particular from 55 to 75% by weight, of the principal
component A,
[0064] from 0 to 55% by weight, preferably from 0 to 30% by weight
and in particular from 5 to 20% by weight, of the ancillary
component B, and
[0065] from 0 to 55% by weight, preferably from 5 to 40% by weight
and in particular from 10 to 35% by weight, of the ancillary
component C,
[0066] where at least one of the fractions forming the principal
component A has a ratio between weight-average (M.sub.w) and
number-average (M.sub.n) molar masses of the polymers
M.sub.w/M.sub.n>4.5, preferably >5 and in particular >6.
The fractions forming the principal component A and having a ratio
M.sub.w/M.sub.n>4.5 preferably make up at least 10% by weight,
in particular at least 20% by weight and very particularly
preferably at least 30% by weight, of the principal component
A.
[0067] In this embodiment, the semicrystalline propylene polymer
compositions therefore have broad molar mass distribution of the
highly isotactic fractions. Compared with conventional
polypropylenes used for producing BOPP films, they achieve, for
example, better mechanical properties in the films and better
barrier properties, without giving any disadvantages in
processibility.
[0068] In another embodiment of the present invention, the
semicrystalline propylene polymer compositions can be broken down
into
[0069] from 40 to 85% by weight, preferably from 45 to 75% by
weight and in particular from 50 to 70% by weight, of the principal
component A,
[0070] from 15 to 55% by weight, preferably from 15 to 45% by
weight and in particular from 20 to 35% by weight, of the ancillary
component B, and
[0071] from 0 to 40% by weight, preferably from 5 to 35% by weight
and in particular from 5 to 30% by weight, of the ancillary
component C,
[0072] where the room-temperature xylene-soluble fraction X.sub.L
in the semicrystalline propylene polymer composition is not more
than 5% by weight, preferably not more than 4% by weight.
Particularly preferred propylene polymer compositions of this
embodiment have a fraction X.sub.L which is not more than 3% by
weight.
[0073] The semicrystalline propylene polymer compositions of this
embodiment have a relatively high content of low-tacticity
fractions which are soluble in xylene at (T.sub.M/2)+7.5.degree. C.
but not at room temperature and have small room-temperature
xylene-soluble fractions. Compared with conventional polypropylenes
used for producing BOPP films, they have better processibility,
reflected in greater temperature- and speed-latitude during
processing, and better optical properties, without any
disadvantages for the mechanical properties of the films.
[0074] The substantial factor in relation to the properties of the
novel propylene polymer compositions is their content of components
A, B and C. The process which prepared the respective mixtures of
differing polymer chains is not critical per se.
[0075] For example, two or more starting polymers may be
polymerized separately and then mixed using suitable mixing
equipment, such as screw extruders, Diskpack plasticators, kneaders
or roll mills.
[0076] However, the propylene polymer compositions are preferably
not polymerized separately. In that case it is possible to use a
mixture of two or more different catalysts which, under the
polymerization conditions established, deliver different
polypropylenes, or to use a catalyst which in itself has different
active centers, so that the catalyst itself delivers appropriate
mixtures of polymer chains. Another way is to polymerize in various
reactors, for example in a reactor cascade, under conditions
sufficiently different to give the desired composition as final
product.
[0077] The constituents of the novel propylene polymer composition,
or the entire propylene polymer composition, may be produced in a
known manner in bulk, in suspension or in the gas phase, in the
usual reactors used for polymerizing propylene, either batchwise or
preferably continuously, in one or more stages. The polymerizations
are generally carried out at from 20 to 150.degree. C. and at
pressures of from 1 to 100 bar with average residence times of from
0.5 to 5 hours, preferably at from 60 to 90.degree. C. and at
pressures of from 20 to 35 bar and with average residence times of
from 0.5 to 3 hours.
[0078] Use is made here in particular of the Ziegler-Natta catalyst
systems usual in polymerization technology. These are generally
composed of a titanium-containing solid component, the preparation
of which frequently uses, besides titanium compounds, inorganic or
polymeric fine-particle supports, compounds of magnesium, halogen
compounds and electron-donor compounds, and of at least one
cocatalyst. Aluminum compounds may be used as cocatalysts. Besides
an aluminum compound, it is preferable for one or more
electron-donor compounds to be used as further cocatalysts.
[0079] The propylene polymers may also be prepared using catalyst
systems based on metallocene compounds. For the purposes of the
present invention, metallocenes are complex compounds made from
metals of transition groups of the Periodic Table with organic
ligands, and these together with metallocenium-ion-forming
compounds give effective catalyst systems.
[0080] The central atom present in the metallocenes usually used is
titanium, hafnium or preferably zirconium, and the central atom
generally has bonding via a .pi. bond to at least one, generally
substituted, cyclopentadienyl group. The metallocene complexes are
frequently in supported form in the catalyst systems. The
metallocenium-ion-forming compounds present in the metallocene
catalyst systems are moreover usually aluminoxane compounds or
strong, neutral Lewis acids, ionic compounds with Lewis-acid
cations or ionic compounds with Bronsted acids as cation.
[0081] The novel semicrystalline propylene polymer composition
preferably has a molar mass (weight average M.sub.w) of from 50,000
to 800,000 g/mol. Its melt flow rate at 230.degree. C. under a load
of 2.16 kg to ISO 1133 is from 0.1 to 100 g/10 min, preferably from
0.5 to 50 g/10 min and in particular from 1 to 10 g/10 min.
[0082] It is usual for customary amounts of conventional additives,
such as stabilizers, lubricants, mold-release agents, fillers,
nucleating agents, antistats, plasticizers, dyes, pigments or flame
retardants to be added to the novel semicrystalline propylene
polymer composition prior to its use. These are usually
incorporated into the polymer during pelletization of the
polymerization product produced in pulverulent form.
[0083] The usual stabilizers are antioxidants, such as sterically
hindered phenols, process stabilizers, such as phosphites or
phosphonites, acid scavengers, such as calcium stearate, zinc
stearate or dihydrotalcite, sterically hindered amines, or else UV
stabilizers. The novel propylene polymer composition generally
comprises amounts of up to 2% by weight of one or more of the
stabilizers.
[0084] Examples of suitable lubricants and mold-release agents are
fatty acids, the calcium or zinc salts of the fatty acids, fatty
amides and low-molecular-weight polyolefin waxes, and these are
usually used in concentrations of up to 2% by weight.
[0085] Examples of fillers which may be used for the propylene
polymer composition are talc, chalk and glass fibers, and the
amounts which may be used here are up to 50% by weight.
[0086] Examples of suitable nucleating agents are inorganic
additives, such as talc, silica or kaolin, salts of mono- or
polycarboxylic acids, such as sodium benzoate or aluminum
tert-butylbenzoate, dibenzylidenesorbitol or its
C.sub.1-C.sub.8-alkyl-substituted derivatives, such as methyl- or
dimethyldibenzylidenesorbitol, and salts of diesters of phosphoric
acid, such as sodium 2,2'-methylenebis(4,6-di-t- ert-butylphenyl)
phosphate. The content of nucleating agents in the propylene
polymer composition is generally up to 5% by weight.
[0087] Additives of this type are generally commercially available
and are described, for example, in Gachter/Muller, Plastics
Additives Handbook, 4th Edition, Hansa Publishers, Munich,
1993.
[0088] The good performance characteristics of the novel
semicrystalline propylene polymer compositions make them especially
suitable for producing films, fibers or moldings and in particular
for producing biaxially stretched films.
[0089] The invention also provides biaxially stretched films
produced from the novel semicrystalline propylene polymer
compositions and having a stretching ratio of at least 1:3
longitudinally and of at least 1:5 transversely.
[0090] Biaxially stretched films may be produced by melt extrusion
of the propylene polymer composition, whereupon the discharged melt
is first cooled to between 100 and 20.degree. C. for
solidification, and the solidified film is then stretched
longitudinally at from 80 to 150.degree. C. with a stretching ratio
of at least 1:3 and transversely at from 120 to 170.degree. C. with
a stretching ratio of at least 1:5.
[0091] To this end, the semicrystalline propylene polymer
compositions are melted at from 220 to 300.degree. C., preferably
from 240 to 280.degree. C., for example, in an extruder, where
other additives or polymers may be added in the extruder, and the
melt is extruded through a slot die or an annular die.
[0092] The resultant film is then solidified by cooling. By
extrusion through a slot die (flat-film die) the cooling generally
takes place via one or more take-off rolls whose surface
temperature is from 10 to 100.degree. C., preferably from 15 to
70.degree. C., for example. If an annular die is used, the film
bubble is usually cooled by air or water at from 0 to 40.degree.
C.
[0093] The resultant film is then stretched longitudinally and
transversely to the direction of extrusion, orienting the molecular
chains. The sequence of stretching is not critical. In
flat-film-die extrusion the first stretching is generally
longitudinal, carried out with the aid of two or more pairs of
rolls running at different speeds corresponding to the desired
stretching ratio. This is followed by transverse stretching using
appropriate equipment comprising clips. It is also possible for the
longitudinal and transverse stretching to take place simultaneously
using suitable equipment comprising clips. If an annular die is
used, stretching in both directions usually takes place
simultaneously by injection of gas into the film bubble.
[0094] Prior to the stretching of the film, it may be heated to
between 60 and 110.degree. C., for example. The longitudinal
stretching preferably takes place at from 80 to 150.degree. C., in
particular from 100 to 130.degree. C., and the transverse
stretching at from 120 to 190.degree. C., in particular from 145 to
180.degree. C. The longitudinal stretching ratio is generally at
least 1:3, preferably from 1:4 to 1:7 and in particular from 1:4.5
to 1:5. The transverse stretching ratio is generally at least 1:5,
preferably from 1:6 to 1:12 and in particular from 1:7 to 1:10.
[0095] The biaxial stretching may be followed by a heat treatment
for thermosetting, in which the film is held at from 100 to
160.degree. C. for from about 0.1 to 10 s. The film is then wound
up in the usual manner by wind-up equipment.
[0096] During or after production of the BOPP film, one or both
surfaces may be corona- or flame-treated by one of the known
methods, or, if required, metallized, for example with
aluminum.
[0097] It is also possible for the novel semicrystalline propylene
polymer composition to form just one layer, or just some of the
layers, of a multilayer biaxially stretched film.
[0098] The biaxially stretched films produced from the novel
semicrystalline propylene polymer compositions have in particular
excellent stiffness, excellent barrier action and excellent
transparency.
EXAMPLES
[0099] The following tests were carried out to characterize the
specimens:
[0100] Determination of average particle diameter:
[0101] To determine the average particle diameter of the silica gel
the particle size distribution of the silica gel particles was
determined by Coulter Counter Analysis to ASTM D 4438 and the
volume-based average (median) calculated from the results.
[0102] Determination of pore volume:
[0103] By mercury porosimetry to DIN 66133
[0104] Determination of specific surface area:
[0105] By nitrogen adsorption to DIN 66131
[0106] Determination of water content:
[0107] To determine the water content, 5 g of silica gel were dried
for 15 min at 160.degree. C. at atmospheric pressure (constant
weight). The weight loss corresponds to the initial water
content.
[0108] Determination of ethylene content:
[0109] The ethylene content was determined by .sup.13C NMR
spectroscopy on polymer pellets.
[0110] Determination of melt flow rate (MFR):
[0111] to ISO 1133 at 230.degree. C. under a load of 2.16 kg.
[0112] Determination of T.sub.M:
[0113] The melting point T.sub.M was determined by DSC to ISO 3146
using a first heating procedure with a heating rate of 20.degree.
C. per minute to 200.degree. C., dynamic crystallization at a
cooling rate of 20.degree. C. per minute to 25.degree. C. and a
second heating procedure with a heating rate of 20.degree. C. per
minute, again to 200.degree. C. The melting point T.sub.M is then
the temperature of the maximum in the plot of enthalpy against
temperature measured during the second heating procedure.
[0114] TREF fractionation:
[0115] The solvent used comprised industrial xylene with less than
0.1% by weight of nonvolatile fractions, and with 5 grams per liter
of 2,6-di-tert-butyl-4-methylphenol added as stabilizer. For each
fractionation, 5 g of the propylene polymer composition were
dissolved in 400 ml of boiling xylene, and the solution was then
cooled linearly at a cooling rate of 10.degree. C./h to 25.degree.
C., whereupon most of the polymer precipitated.
[0116] The crystalline suspension was transferred into the 500 ml
temperature-controllable extraction apparatus shown in FIG. 1 and
heated to the first elution temperature: (T.sub.M/2)+7.5.degree. C.
Before measurements were made the entire apparatus was flushed with
nitrogen. The gas space above the extraction liquids remained under
nitrogen during the extraction. The polypropylene crystals were
extracted for 15 minutes at this temperature with vigorous mixing.
The polymer solution was then run off, while the polypropylene
crystals remained in the extractor. The dissolved polymer was
precipitated in cold acetone (<0.degree. C.), filtered off and
dried for from 4 to 5 hours at 100.degree. C. in vacuo.
[0117] The extractor was then heated to the next elution
temperature in the temperature sequence 70.degree. C., 75.degree.
C., 80.degree. C., 85.degree. C., 90.degree. C., 94.degree. C.,
98.degree. C., 102.degree. C., 107.degree. C., 112.degree. C.,
117.degree. C., 122.degree. C. and 400 ml of xylene at the same
temperature were added. Extraction was repeated for 15 minutes with
vigorous mixing, the polymer solution was run off, and the
dissolved polymer was precipitated in cold acetone, filtered off
and dried. These steps were repeated until all of the propylene
homopolymer had dissolved.
[0118] The content calculated for each TREF fraction gives the
content which has dissolved during the extraction at the
temperature given. The % by weight data here are based on the
initial sample weight of 5 g. As a result of losses during weighing
and filtration, therefore, the total of the fractions is in each
case not quite 100% by weight.
[0119] Gel permeation chromatography (GPC):
[0120] The gel permeation chromatography (GPC) at 145.degree. C.
was carried out at 145.degree. C. in 1,2,4-trichlorobenzene using a
Waters 150C GPC apparatus. The data were evaluated using Win-GPC
software from HS-Entwicklungsgesellschaft fur wissenschaftliche
Hardund Software mbH, Ober-Hilbersheim, Germany. The columns were
calibrated using polypropylene standards with molar masses of from
100 to 10.sup.7 g/mol.
[0121] The weight-average (M.sub.w) and number-average (M.sub.n)
molar masses of the polymers were determined. The value Q is the
ratio of the weight average (M.sub.w) to the number average
(M.sub.n).
[0122] Determination of the proportions of components A, B and
C:
[0123] A TREF analysis was carried out with the propylene polymer
composition to be studied. In the evaluation which followed, the
fractions taken into consideration were all of those whose
proportion by weight was more than 1%. The molar mass distribution
of all of the fractions to be taken into consideration was
determined using GPC.
[0124] The proportion by weight of the ancillary component B is the
proportion by weight of the fraction which was obtained at the
first elution temperature, i.e. at (T.sub.M/2)+7.5.degree. C.
[0125] The proportion by weight of the principal component A is the
proportion by weight of all of the fractions obtained at higher
elution temperatures and having an average molar mass M.sub.n
(number average).gtoreq.120,000 g/mol.
[0126] The ancillary component C is formed by all of the fractions
obtained at temperatures higher than (T.sub.M/2)+7.5.degree. C. and
having an average molar mass M.sub.n (number average)<120,000
g/mol.
[0127] The difference Z, where
z=100% by weight-(A+B+C)
[0128] quantifies those fractions of the propylene polymer
composition initially weighed which were not taken into
consideration in calculating the amounts of components A, B and C
because of losses occurring during TREF or because the amounts of
particular fractions were below the limit.
[0129] Determination of processing latitude:
[0130] During production of the BOPP films the stretching
temperature was varied to determine the temperature range within
which BOPP films can be obtained. This temperature range has a
higher-temperature limit resulting from tearing of the film due to
melting, and has a lower-temperature limit resulting from tearing
of the film due to inhomogeneity caused by incomplete melting, or
from solidification of the film to the extent that it slips out of
the orienting equipment.
[0131] The procedure was to begin with a processing temperature
which ensured stable running. The stretching temperature was then
raised in steps of 2.degree. C. until the film tore. The next
temperature was set here as soon as 1000 m of film could be
produced at one temperature without tearing. Then, again starting
at the initial temperature, the stretching temperature was lowered
in steps of 2.degree. C. until the film again tore or slipped out
of the orienting equipment.
[0132] Determination of maximum take-off speed:
[0133] During production of the BOPP films the take-off speed was
varied to establish the range within which BOPP films can be
obtained. This range has a higher-speed limit as a result of
tearing of the film due to inhomogeneity or to excessive
tension.
[0134] The procedure was to begin at a take-off speed which ensured
stable running (the stretching temperature here was 160.degree.
C.). The take-off speed was then increased in steps of 25 m/min
until the film tore. The next speed here was established once 1000
m of film could be produced at one speed without tearing.
[0135] Determination of modulus of elasticity (tensile modulus of
elasticity):
[0136] Longitudinal and transverse strips of width 15 mm were cut
out from biaxially stretched films and used to determine the
tensile modulus of elasticity to ISO 527-2 at 23.degree. C.
[0137] Determination of haze:
[0138] To ASTM D-1003.
[0139] Determination of water vapor barrier properties
[0140] H.sub.2O permeability measured to DIN 53122.
[0141] Determination of oxygen barrier properties
[0142] O.sub.2 permeability measured to ASTM D3985-81.
Example 1
[0143] a) Preparation of a titanium-containing solid component
[0144] A fine-particle spherical silica gel prepared by spray
drying and having an average particle diameter of 45 .mu.m, a pore
volume of 1.5 cm.sup.3/g, a specific surface area of 260 m.sup.2/g
and a water content of 2.7% by weight was mixed with a solution of
n-butyloctylmagnesium in n-heptane, using 0.3 mol of the magnesium
compound per mole of SiO.sub.2. The solution was stirred for 45
minutes at 95.degree. C., then cooled to 20.degree. C., and, based
on the organomagnesium compound, ten times the molar amount of
hydrogen chloride was passed into the mixture. After 60 minutes the
reaction product was mixed with 3 mol of ethanol per mole of
magnesium, with constant stirring. This mixture was stirred for 0.5
hour at 80.degree. C. and then mixed with, based in each case on 1
mol of magnesium, 7.2 mol of titanium tetrachloride and 0.5 mol of
di-n-butyl phthalate. This was followed by stirring for 1 hour at
100.degree. C., filtering off the resultant solid and washing
several times with ethylbenzene.
[0145] The resultant solid product was extracted for 3 hours at
125.degree. C. with a 10% strength by volume solution of titanium
tetrachloride in ethylbenzene. The solid product was then separated
from the extraction medium by filtration and washed with n-heptane
until the remaining content of titanium tetrachloride in the
extraction medium was only 0.3% by weight.
[0146] The titanium-containing solid component comprised
[0147] 3.5% by weight of Ti
[0148] 7.4% by weight of Mg
[0149] 28.2% by weight of Cl.
[0150] b) Polymerization
[0151] The polymerization was carried out in a continuously
operated cascade of two vertically agitated gas-phase reactors each
with a useful volume of 200 1 and arranged in series, both reactors
comprising a moving solid bed of fine-particle polymer. The
catalyst system used was one made from the titanium-containing
solid component prepared in Example la) and also from the further
components triethylaluminum and dicyclopentyldimethoxysilane.
[0152] Gaseous propylene, the titanium-containing solid component,
and also triethylaluminum and dicyclopentyldimethoxysilane, were
passed into the first gas-phase reactor. The amount of
triethylaluminum added here was set at 210 mmol per g of
titanium-containing solid component, and the amount of
dicyclopentyldimethoxysilane was set at 0.02 mol per mole of
triethylaluminum. Any addition of hydrogen as molar-mass regulator
was completely dispensed with. The polymerization took place at a
pressure of 28 bar and at 80.degree. C.
[0153] The propylene homopolymer obtained in the first gas-phase
reactor was transferred into the second gas-phase reactor together
with catalyst constituents which were still active, and the
polymerization was continued there at a pressure of 20 bar and at
70.degree. C. Hydrogen was passed into the second reactor in
sufficient amounts to give a constant proportion of 11% by volume
of hydrogen in the gas space. During this procedure, the
composition of the gas was determined using a gas chromatograph at
intervals of five minutes and regulated by tracking the amounts
fed. Dicyclopentyldimethoxysilane was moreover again added in the
second reactor in amounts sufficient for the total amount of
dicyclopentyldimethoxysilane added to be 0.1 mol per mole of
triethylaluminum.
[0154] The output from the reactor cascade was adjusted to 48 kg/h
via the amount of the titanium-containing solid component fed. The
productivity obtained was 13,300 g of polymer per g of
titanium-containing solid component.
[0155] During pelletization, a stabilizer usually used for
propylene polymers and based on tetrakis(methylene
3,5-di-tert-butylhydroxyhydrocin- namate)methane and
tris(2,4-di-tert-butylphenyl) phosphite was incorporated. The
resultant propylene polymer composition had a melting point of
165.degree. C., a melt flow rate of 2.1 g/10 min and a
room-temperature xylene-soluble fraction of 3.1% by weight. It was
broken down into the fractions given in Table 1 by TREF. The yield
from the fractionation, i.e. the total of the proportions by weight
of the fractions, was 99.5% by weight.
1TABLE 1 Average molar mass Proportion of fraction Elution by
weight (number temperature [% by average M.sub.n) Fraction
[.degree. C.] weight] [g/mol] M.sub.2/M.sub.n 1 90 7.3 13800 5.6 2
94 2.0 17800 2.3 3 98 3.6 22900 2.0 4 102 8.9 36000 2.3 5 107 14.7
49300 2.4 6 112 37.7 144300 4.7 7 117 13.6 126300 6.2 8 122 8.8
247800 3.5 9 125 2.9 272300 3.6
[0156] Since (T.sub.M/2)+7.5.degree. C. was 90.degree. C. for the
propylene polymer composition studied the first fraction was eluted
at 90.degree. C. Fractions 2 to 5 at 94, 98, 102 and 107.degree. C.
together form component C and fractions 6 to 9 at 112, 117, 122 and
125.degree. C. form component A. This therefore gave a composition
made of
[0157] Principal component A: 63.0% by weight
[0158] Ancillary component B: 7.3% by weight, and
[0159] Ancillary component C: 29.2% by weight.
[0160] The difference Z was therefore 0.5% by weight.
[0161] c) Production of a BOPP film
[0162] The semicrystalline propylene polymer composition obtained
was used to produce a biaxially stretched film of thickness about
20 .mu.m. The film was produced on a Bruckner Maschinenbau pilot
plant with a 1.3 m flat-film die. The throughput was 150 kg/h. The
extruded film was cooled to 40.degree. C. and the solidified film
stretched longitudinally at 116.degree. C. with a stretching ratio
of 4.5:1 and transversely at 157.degree. C. with a stretching ratio
of 8:1. The properties of the biaxially stretched film produced can
be found in Table 3 below.
Example 2
[0163] a) Preparation of a titanium-containing solid component
[0164] The catalyst solid prepared in Example 1a) was used.
[0165] b) Polymerization
[0166] The polymerization took place in the reactor cascade also
used in Example 1b) with a catalyst system made from the
titanium-containing solid component prepared in Example 1a) and the
further components triethylaluminum and
dicyclopentyldimethoxysilane.
[0167] Gaseous propylene, the titanium-containing solid component,
and also triethylaluminum and dicyclopentyldimethoxysilane, were
passed into the first gas-phase reactor. The amount of
triethylaluminum added here was set at 210 mmol per g of
titanium-containing solid component, and the amount of
dicyclopentyldimethoxysilane was set at 0.1 mol per mole of
triethylaluminum. Any addition of hydrogen as molar-mass regulator
was completely dispensed with. The polymerization took place at a
pressure of 28 bar and at 80.degree. C.
[0168] The propylene homopolymer obtained in the first gas-phase
reactor was transferred into the second gas-phase reactor together
with catalyst constituents which were still active, and in this
reactor a mixture of propylene and ethylene was continuously
polymerized onto the homopolymer at a pressure of 20 bar and at
70.degree. C. The polymerization in the second reactor also took
place in the presence of hydrogen. The amounts of ethylene and
hydrogen passed into the mixture were sufficient to give a constant
proportion of 3% by volume of ethylene and 17% by volume of
hydrogen in the gas space. During this procedure, the composition
of the gas was determined using a gas chromatograph at intervals of
five minutes and regulated by tracking the amounts fed.
[0169] The output from the reactor cascade was adjusted to 44 kg/h
via the amount of the titanium-containing solid component fed. The
productivity obtained was 17,400 g of polymer per g of
titanium-containing solid component.
[0170] During pelletization, a stabilizer usually used for
propylene polymers and based on tetrakis(methylene
3,5-di-tert-butylhydroxyhydrocin- namate)methane and
tris(2,4-di-tert-butylphenyl) phosphite was incorporated. The
resultant propylene polymer composition had a melting point of
163.2.degree. C., a melt flow rate of 2.2 g/10 min and a
room-temperature xylene-soluble fraction of 3.4% by weight. The
ethylene content was 1.5% by weight. It was broken down into
fractions by TREF. The yield from the fractionation was 97.2% by
weight.
[0171] This gave a composition made of
[0172] Principal component A: 60.7% by weight
[0173] Ancillary component B: 28.2% by weight, and
[0174] Ancillary component C: 8.3% by weight.
[0175] The difference Z was therefore 2.8% by weight.
[0176] The maximum ratio M.sub.w/M.sub.n of the fractions forming
component A was 3.7.
[0177] c) Production of a BOPP film
[0178] The semicrystalline propylene polymer composition obtained
was used to produce a biaxially stretched film of thickness about
20 .mu.m. The film was produced on a Bruckner Maschinenbau pilot
plant with a 1.3 m flat-film die. The throughput was 150 kg/h. The
extruded film was cooled to 40.degree. C. and the solidified film
stretched longitudinally at 116.degree. C. with a stretching ratio
of 4.5:1 and transversely at 157.degree. C. with a stretching ratio
of 8:1. The properties of the biaxially stretched film produced can
be found in Table 3 below.
Comparative Example A
[0179] A biaxially stretched film of thickness about 20 .mu.m was
produced as in Example 1 with a propylene homopolymer used
commercially for OPP film production (Novolen.RTM. 1104 K from
Targor GmbH).
[0180] A melting point of 165.5.degree. C., a melt flow rate of 3.2
g/10 min and a room-temperature xylene-soluble fraction of 3.2% by
weight were determined for the Novolen.RTM. 1104 K used. It was
broken down by TREF into the fractions given in Table 2. The yield
of the fractionation was 96.7% by weight.
2TABLE 2 Average molar mass Proportion of fraction Elution by
weight (number temperature [% by average M.sub.n) Fraction
[.degree. C.] weight] [g/mol] M.sub.2/M.sub.n 1 90.25 4.6 27200 3.4
2 94 1.6 38900 2.1 3 98 2.6 39400 1.9 4 102 3.9 46300 1.7 5 107 9.3
66300 1.9 6 112 48.7 156600 2.6 7 117 25.3 185900 2.6 8 122 0.7 --
--
[0181] Since (T.sub.M/2)+7.5.degree. C. was 90.25.degree. C. for
the propylene polymer composition studied, the first fraction was
eluted at this temperature. Fractions 2 to 5 at 94, 98, 102 and
107.degree. C. together form component C, and fractions 6 and 7 at
112 and 117.degree. C. form component A. The proportion by weight
of fraction 8 was below 1% by weight. This fraction is therefore
part of Z. This therefore gave a composition made of
[0182] Principal component A: 74.0% by weight
[0183] Ancillary component B: 4.6% by weight, and
[0184] Ancillary component C: 17.4% by weight.
[0185] The difference Z was therefore 4.0% by weight.
[0186] The film properties can be found in Table 3 below.
Comparative Example B
[0187] A biaxially stretched film of thickness about 20 .mu.m was
produced as in Example 1 with a propylene homopolymer used
commercially for OPP film production (Novolen.RTM. NQ 10134 from
Targor GmbH).
[0188] A melting point of 163.1.degree. C., a melt flow rate of 3.4
g/10 min and a room-temperature xylene-soluble fraction of 3.5% by
weight were determined for the Novolen.RTM.NQ 10134 used. It was
broken down by TREF into fractions. The yield of the fractionation
was 97.2% by weight.
[0189] This gave a composition made of
[0190] Principal component A: 67.0% by weight,
[0191] Ancillary component B: 8.2% by weight, and
[0192] Ancillary component C: 22.0% by weight.
[0193] The difference Z was therefore 2.8% by weight.
[0194] The maximum ratio M.sub.w/M.sub.n for the fractions forming
component A was 2.5.
Comparative Example C
[0195] A biaxially stretched film of thickness about 20 .mu.m was
produced as in Example 1 with a random propylene-ethylene copolymer
used commercially for OPP film production (Novolen.RTM. NX 10094
from Targor GmbH).
[0196] A melting point of 155.7.degree. C., a melt flow rate of 2.9
g/10 min, a room-temperature xylene-soluble fraction of 1.7% by
weight and an ethylene content of 1.1% by weight were determined
for the Novolen.RTM. NX 10094 used. It was broken down into the
fractions by TREF. The yield of the fractionation was 99.7% by
weight.
[0197] This gave a composition made of
[0198] Principal component A: 88.2% by weight,
[0199] Ancillary component B: 7.7% by weight, and
[0200] Ancillary component C: 3.8% by weight.
[0201] The difference Z was therefore 0.3% by weight.
[0202] The maximum ratio M.sub.w/M.sub.n for the fractions forming
component A was 2.8.
[0203] Table 3 below gives the properties of the biaxially
stretched films manufactured from the semicrystalline propylene
polymer compositions prepared by way of example.
3 TABLE 3 Comp. Comp. Comp. Example Example Ex. Ex. Ex. 1 2 A B C
Processing latitude 11 18 12 11 13 [.degree. C.] Maximum take-off
100 >200 100 150 100 speed [m/min] Longitudinal 2600 2000 2200
2000 2200 modulus of elasticity [MPa] Transverse modulus 4800 4300
4700 4500 4600 of elasticity [MPa] Haze [%] 2.4 1.1 2.0 1.6 2.2
H.sub.2O permeability 0.27 0.28 0.28 0.29 0.28 [g 100
.mu.m/(m.sup.2 d)] O.sub.2 permeability 410 430 430 440 430
[cm.sup.3 100 .mu.m/ (m.sup.2 d bar)]
[0204] From a comparison of the examples with the comparative
examples it can be seen that the propylene polymer composition of
Example 1 in particular has a broader molar mass distribution, i.e.
an increased ratio M.sub.w/M.sub.n in the principal component A,
and the propylene polymer composition of Example 2 has an increased
proportion of ancillary component B.
[0205] Comparison of Example 2 with Comparative Example C shows
that the incorporation of ethylene cannot by itself produce
propylene polymer compositions whose distribution accords with the
invention. This is also apparent from the fact that incorporating
1.1% by weight of ethylene in Comparative Example C lowers the
melting point to 155.7.degree. C., whereas in Example 2 the melting
point can be held at 163.2.degree. C. despite an ethylene content
of 1.5% by weight.
[0206] It can be seen from Table 3 that the propylene polymer
composition of Example 1 can in particular give better mechanical
properties without any loss of processibility. There is also an
improvement in barrier properties (lower permeability to water
vapor and oxygen). The propylene polymer composition of Example 2
has better processibility and better optical properties (lower
haze) without any need to accept impairment of the mechanical
properties of the films or of their barrier properties.
* * * * *